Southern Company Services ATCID Version 1.2 Available Transfer Capability Implementation Document (ATCID) ATCID Revision Log

Transcription

1 Available Transfer Capability Implementation Document (ATCID) ATCID Revision Log Date Description of Change 3/30/11 Initial Version (Version 1) 2/20/12 Enhancements to Attachment B (Version 1.1) 12/17/13 Update and clarify language, reflect modifications of ATC paths due to integration of SMEPA and Entergy to MISO (Version 1.2) PURPOSE: To ensure that calculations are performed by Southern Company Services, Inc. (SCS) to maintain awareness of available transmission system capability and future flows on SCS s system as well as SCS s neighbors and to increase consistency and reliability in the development and documentation of Transfer Capability calculations for short-term use to support analysis and system operations. 1. SCS selects the Area Interchange Methodology for calculating Available Transfer Capability (ATC) for each ATC Path (Attachment A) per time period identified for facilities within its transmission operating area. 2. SCS prepares and keeps current this Available Transfer Capability Implementation Document (ATCID) that includes, at a minimum, the following information in Attachments B, D, E or F: 2.1. Information describing how the Area Interchange Methodology has been implemented in such detail that, given the same information used by SCS (e.g. transfer capability, existing transmission commitments, reliability margins, postbacks, counterflows, etc.), the results of the ATC calculations can be validated (Attachment B) A description (Attachment B) of the manner in which SCS accounts for counterflows including: How confirmed transmission reservations, expected Interchange and internal counterflows are addressed in firm and non-firm ATC calculations The rationale for the accounting specified in The identity of Transmission Operators and Transmission Service Providers from which SCS receives data for use in calculating ATC (Attachment D) The identity of the Transmission Service Providers and Transmission Operators to which it provides data for use in calculating transfer capability (Attachment E) A description of the allocation processes listed below that are applicable to SCS: Processes used to allocate transfer capability among multiple lines or subpaths within a larger ATC Path. (Not Applicable) Processes used to allocate transfer capabilities among multiple owners or users of an ATC Path. (Attachment F): Effective: December 17, 2013 Page 1 of 24

2 Processes used to allocate transfer capabilities between Transmission Service Providers to address issues such as forward looking congestion management and seams coordination. (Not Applicable) 2.6. A description (Attachment B) of how generation and transmission outages are considered in transfer capability calculations, including: The criteria used to determine when an outage that is in effect part of a day impacts a daily calculation The criteria used to determine when an outage that is in effect part of a month impacts a monthly calculation How outages from other Transmission Service Providers that can not be mapped to the transmission model used to calculate transfer capability are addressed. 3. SCS includes in this ATCID, at a minimum, the following information relative to its methodology for determining Total Transfer Capability (TTC): 3.1. Information describing how the selected methodology has been implemented, in such detail that, given the same information used by SCS (power flow model, subsystem files, contingency list, monitored elements, exclude file, interchange spreadsheet, etc.), the results of the TTC calculations can be validated (Attachment B) A description of the manner in which SCS will account for Interchange Schedules in the calculation of TTC (Attachment B) Any contractual obligations for allocation of TTC (Attachment F) A description of the manner in which contingencies are identified for use in the TTC process (Attachment B) The following information on how source and sink for transmission service is accounted for in ATC calculations: Define if the source used for Available Transfer Capability (ATC) calculations is obtained from the source field or the Point of Receipt (POR) field of the transmission reservation (Attachment B) Define if the sink used for ATC calculations is obtained from the sink field or the Point of Delivery (POD) field of the transmission reservation (Attachment B) The source/sink or POR/POD identification and mapping to the model (Attachment B). Effective: December 17, 2013 Page 2 of 24

3 Attachment A: List of ATC Paths 1 1. AEC-SOCO 2. DUK-SOCO 3. MISO-SOCO 4. FL-SOCO 5. SC-SOCO 6. SCEG-SOCO 7. SOCO-AEC 8. SOCO-DUK 9. SOCO-MISO 10. SOCO-FL 11. SOCO-SC 12. SOCO-SCEG 13. SOCO-SOCO SOCO-TVA 15. TVA-SOCO 1 Southeastern Power Administration (SEPA) is responsible for marketing electric power generated by hydroelectric facilities owned by the United States Army Corps of Engineers. These plants are located in generation-only control areas, and thus MW produced by these facilities are transmitted from one Balancing Authority Area to another. However, for TTC purposes, any transaction that has a POR or POD of a SEPA plant interconnected to the Southern Balancing Authority Area will use either SOCO, DUKE (Hartwell) or SC (Russell, Thurmond) as the POR or POD. Thus, for the purpose of defining ATC Paths, SEPA plant designations shall use SOCO, DUKE, or SC. Neither SEPA nor the Corps of Engineers is registered with NERC as a Transmission Service Provider. Therefore, SEPA and the Corps of Engineers are not required to develop an ATCID or calculate ATCs. 2 The SOCO-SOCO pathname listed on Southern Companies OASIS does not represent a traditional Balancing Area to Balancing Area interconnection. This pseudo-path exists primarily to facilitate the designation of network resources by the Transmission Provider on behalf of its Native Load Customers, and the reservation of capacity for future load growth. Since this pseudo-path represents a large number of source points to a large number of sink points, all within the Southern Balancing Area, calculating a TTC and resultant ATC for this pseudo-path is not appropriate or practicable. Instead, SCS sets the TTC value for this pseudo-path equal to the forecasted peak load value. Effective: December 17, 2013 Page 3 of 24

4 Attachment B: Area Interchange Methodology Used to Calculate Southern Balancing Authority ATC and TTC 1. Available Transfer Capability Calculations SCS calculates Available Transfer Capability (ATC) using mathematical formulas that are consistent with the current version of NERC standard MOD-028 Area Interchange Methodology. When calculating firm ATC for an ATC Path, SCS uses the following formula: ATC F = TTC ETC F CBM TRM + Postbacks F + counterflows F Where: ATC F is the firm Available Transfer Capability for the ATC Path for that period. TTC is the Total Transfer Capability of the ATC Path for that period. ETC F is the sum of existing firm transmission commitments for the ATC Path during that period. CBM is the Capacity Benefit Margin for the ATC Path during that period. TRM is the Transmission Reliability Margin for the ATC Path during that period. Postbacks F are changes to firm ATC due to a change in the use of Transmission Service for that period, as defined in Attachment C of Southern Companies OATT. counterflows F are adjustments to firm ATC as determined by SCS and specified in Attachment B, section 2.4. When calculating non-firm ATC for an ATC Path, SCS uses the following formula: ATC NF = TTC ETC F - ETC NF CBM S TRM U + Postbacks NF + counterflows NF Where: ATC NF is the non-firm Available Transfer Capability for the ATC Path for that period. TTC is the Total Transfer Capability of the ATC Path for that period. ETC F is the sum of existing firm transmission commitments for the ATC Path during that period. ETC NF is the sum of existing non-firm transmission commitments for the ATC Path during that period. CBM S is the Capacity Benefit Margin for the ATC Path that has been scheduled without a separate reservation during that period. TRM U is the Transmission Reliability Margin for the ATC Path that has not been released for sale (unreleased) as non-firm capacity by SCS during that period. Postbacks NF are changes to non-firm ATC due to a change in the use of Transmission Service for that period, as defined in Attachment C of Southern Companies OATT. counterflows NF are adjustments to non-firm ATC as determined by SCS and specified in Attachment B, section 2.4. Effective: December 17, 2013 Page 4 of 24

5 When calculating Existing Transmission Commitments for firm commitments (ETC F ) for all time periods for an ATC Path, SCS uses the following algorithm: ETC F = NITS F + GF F + PTP F + ROR F + OS F Where: NITS F is the firm capacity set aside for Network Integration Transmission Service (including the capacity used to serve bundled load within SCS s area with external sources) on ATC Paths that serve as interfaces with other Balancing Authorities. GF F is the firm capacity set aside for Grandfathered Firm Transmission Service and contracts for energy and/or Transmission Service, where executed prior to the effective date of SCS s Open Access Transmission Tariff or safe harbor tariff on ATC Paths that serve as interfaces with other Balancing Authorities. PTP F is the firm capacity reserved for confirmed Point-to-Point Transmission Service. ROR F is the capacity reserved for roll-over rights for Firm Transmission Service contracts granting Transmission Customers the right of first refusal to take or continue to take Transmission Service when the Transmission Customer s Transmission Service contract expires or is eligible for renewal. OS F is the firm capacity reserved for any other service(s), contract(s), or agreement(s) not specified above using Firm Transmission Service, including any other firm adjustments to reflect impacts from other ATC Paths. When calculating ETC for non-firm commitments (ETC NF ) for all time periods for an ATC Path, SCS uses the following algorithm: ETC NF = NITS NF + GF NF + PTP NF + OS NF Where: NITS NF is the non-firm capacity set aside for Network Integration Transmission Service (i.e., secondary service, including the capacity used to serve bundled load within SCS s area with external sources) reserved on ATC Paths that serve as interfaces with other Balancing Authorities. GF NF is the non-firm capacity reserved for Grandfathered Non-Firm Transmission Service and contracts for energy and/or Transmission Service, where executed prior to the effective date of SCS s Open Access Transmission Tariff or safe harbor tariff on ATC Paths that serve as interfaces with other Balancing Authorities. PTP NF is non-firm capacity reserved for confirmed Point-to-Point Transmission Service. OS NF is the non-firm capacity reserved for any other service(s), contract(s), or agreement(s) not specified above using Non-Firm Transmission Service, including any other firm adjustments to reflect impacts from other ATC Paths.. Effective: December 17, 2013 Page 5 of 24

6 ATC is automatically updated by SCS and posted on SCS s OASIS each time (i) TTC values are updated and/or (ii) transmission service is purchased, scheduled, or redirected. ATC values are calculated for each ATC Path, transmission service type and time period using the Area Interchange Methodology for hourly values for at least the next 48 hours, daily values for at least the next 31 calendar days, and monthly values for at least the next 12 months (months 2 13). SCS calculates ATC using the same mathematical algorithm for the scheduling horizon (same day and real-time), operating horizon (day ahead and preschedule) and Operations Planning horizon (beyond the operating horizon up to 13 months). This algorithm is shown on the next page. Effective: December 17, 2013 Page 6 of 24

7 ATC (Path, Service Type and Time Period specific) = TTC (Total Transfer Capability) - Σ ETC (Existing Transmission Commitments at equal or higher service code using the path) 3 - CBM (Capacity Benefit Margin) - TRM (Transmission Reliability Margin) + Σ Postbacks (Unscheduled transmission service commitments and redirected capacity at equal or higher service code linked back to the path) 4 + Σ counterflows 5 The ATC values for the different transmission service types offered on OASIS are calculated using the same algorithm, but certain inputs may vary. These inputs are defined for each of the service types offered and consist of a service code and three logical flags (i.e., whether to apply TRM, whether to apply CBM, and whether to post back unused reserved capacity). Table A below illustrates the configuration for each transmission service type offered on SCS s OASIS. 3 Transmission service types that are assigned service codes for purposes of the ATC algorithm, and such service codes are set forth in Table A. Confirmed reservations utilizing the same path and of equal or higher service code are considered in each calculation. For example, an ATC value is calculated for Monthly Firm Point-To-Point (PTP) transmission service for the path from a particular POR to SOCO by including confirmed reservations of service code 6 and above that utilize that path. Reservations utilizing a different path or of lower service code (e.g., service code 7) would not be included in the calculation. 4 Postbacks are positive adjustments to ATC as defined in Attachment C of Southern Companies OATT. These postbacks may include unscheduled service and redirected services. Unscheduled transmission service commitments are considered in calculating ATC for hourly service. Confirmation of a request to redirect service results in the reduction of ATC on the redirected (new) path and increase of ATC on the original path, at a service type with an equal or lower service code than the new redirected service. For example, if the original service was Monthly Firm PTP (service code 6) and the new redirected service is Daily Firm PTP (service code 10), then ATC will be added back to the original path in the calculation of Daily Firm PTP (service code 10 and below), but not in the calculation of Monthly Firm PTP. At a minimum, redirected capacity is added back to all Hourly services on the original path. 5 Counterflows are the amount of scheduled megawatts (MW) associated with the SCS s customers transactions that will flow in the opposite direction on a path (resulting in a reliable reduction of flow on constrained facilities), that SCS determines can effectively be used to increase ATC. It should be noted that counterflows associated with certain types of constraints (e.g., simultaneous transfer capability limits, voltage limits and stability limits) may not provide relief to constrained facilities required to enable a reliable increase in ATC values. SCS only considers counterflows in the calculation of hourly (non-firm) ATC and when implemented, are included on a manual basis as shown in Figure 1. Effective: December 17, 2013 Page 7 of 24

8 Time Period Class TABLE A ATC Algorithm Configuration Transmission Service Type Service Code Apply TRM Apply CBM Postback Unscheduled Transmission Service Yearly Firm Network 1 Y Y N Yearly Firm Pt-to-Pt 2 Y Y N Yearly Firm Recallable 3 Y Y N Yearly Firm Conditional 4 Y Y N Monthly Firm Network 5 Y Y N Monthly Firm Pt-to-Pt 6 Y Y N Weekly Firm Network 7 Y Y N Weekly Firm Pt-to-Pt 8 Y Y N Daily Firm Network 9 Y Y N Daily Firm Pt-to-Pt 10 Y Y N Daily Secondary Network 11 N N N Hourly Secondary Network 12 N N Y Monthly Non-Firm Pt-to-Pt 13 N N N Weekly Non-Firm Pt-to-Pt 14 N N N Daily Non-Firm Pt-to-Pt 15 N N N Hourly Non-Firm Pt-to-Pt 16 N N Y Hourly Secondary Pt-to-Pt 17 N N Y Effective: December 17, 2013 Page 8 of 24

9 Figure 1. ATC Process Flow Diagram ATC Calculation Specific: Path Service type Time period + TTC Value Transmission Provider s OASIS database Manual Entry Regular updates TTC Study (Southern) - CBM Value Manual Entry seldom changes CBM Study (LSEs) OASIS Postings - TRM Value Manual Entry seldom changes TRM Study (Southern) - ETC Confirmed (Automatic) TSR Processing Frequent Customer Request + Postbacks Redirects (Automatic) Unscheduled from Tagging System (Automatic) Frequent Customer Schedule + Counterflow Manual Entry Customer Opposite direction Schedule This process flow diagram illustrates the various steps through which a single ATC (based upon specific factors) is calculated. Similar ATC calculations are performed for each path, service type, and time period and will generally result in different ATC values specific to those factors. Effective: December 17, 2013 Page 9 of 24

10 2. ATC Components The ATC components are calculated in the operations planning horizon of zero to thirteen months, consistent with the requirements of MOD 001 R Total Transfer Capability (TTC): SCS defines TTC, consistent with the NERC Glossary of Terms Used in Reliability Standards (dated October 26, 2011), as the amount of electric power that can be moved or transferred reliably from one area to another area of the interconnected transmission systems by way of all transmission lines (or paths) between those areas under specified system conditions. Transfer analysis conducted to determine TTC is performed consistent with the principles provided in Transmission Transfer Capability A Reference Document for Calculating and Reporting the Electric Power Transfer Capability of Interconnected Electric Systems dated May, 1995 (hereafter referred to as the NERC TTC reference document ). In addition, SCS uses a TTC calculation approach based on the Area Interchange Methodology. Transfer analysis is performed respecting all applicable System Operating Limits (SOL). Determining Total Transfer Capability (TTC): TTC values in the Southern Balancing Authority Area (SBAA) are evaluated on an aggregated basis, meaning that the transmission facilities of the transmission facility owners located within the SBAA are treated as a combined electrical system in transfer analysis studies. Transfer analysis is performed consistent with the principles provided in NERC TTC reference document and the requirements contained in the current version of MOD-028. The transfer analysis is performed for the 0-13 month horizon on an N-1 basis respecting all applicable SOLs. TTC values in the SBAA are then allocated per the allocation factors to the transmission owners in accordance with Appendix F. Long Term Modeling and Transmission System Topology: SCS participates with SERC members through the SERC Intra-Regional Long Term Study Group (LTSG) to develop yearly power flow cases. This process allows for an aggregation of reduced transmission planning models for each individual system in SERC, in which SCS elects not to reduce any transmission system elements above 100 kv. The resulting LTSG power flow cases incorporate the system topology, facility ratings, generation dispatch, system demands (load forecasts), and transmission uses provided by each SERC participant. The LTSG power flow cases are input into the ERAG Multiregional Modeling Working Group (MMWG) model development processes, which provide the external modeling used in developing the base cases for the SBAA. The base cases for the SBAA are developed by replacing the model of the SBAA found in the LTSG power flow cases with an updated version of the SBAA power flow model. SCS then adds the specific transmission Effective: December 17, 2013 Page 10 of 24

11 service commitments (including partial path reservations) made within the SBAA to create the SBAA Transmission Planning Base Cases which are used to perform reliability planning studies and to evaluate long term transmission service requests. Once the SBAA Transmission Planning Base Cases have been developed, the long term power flow cases are developed as illustrated below. Long Term Power Flow Case Development SBAA Transmission Planning Base Cases SERC LTSG PF Cases Annual Aggregation MMWG PF Cases Updated external models incorporated into base cases Monthly Modeling and Transmission System Topology: SCS participates with SERC members through the SERC Intra-Regional Near Term Study Group (NTSG) to develop quarterly OASIS power flow cases for the upcoming five quarters. These cases are derived from the corresponding yearly SERC LTSG power flow cases. The SERC OASIS power flow cases incorporate the system topology, facility ratings, generation dispatch, system demands (load forecasts), and transmission uses provided by each SERC participant. SCS further updates the quarterly SERC OASIS power flow cases to create thirteen SBAA Monthly power flow cases. These cases include system data provided by adjacent TSPs and/or TOPs identified in Attachment C, on a monthly basis, including updates to system parameters associated with each individual month. SCS also incorporates the specific transmission service commitments (including partial path reservations) made within the SBAA to create the SBAA monthly power flow cases which are used for monthly TTC assessments. Monthly Power Flow Case Development SERC OASIS PF Cases - Quarterly Updates for SBAA and Tier 1 neighbors. SBAA Monthly PF Cases Effective: December 17, 2013 Page 11 of 24

12 Contingencies and Monitoring: In short term analysis (0-13 Months), SCS tests all SBAA contingencies of transmission elements 100 kv and above. SCS also tests all additional facilities that are provided by adjacent entities listed in Attachment C which passed the tests prescribed in MOD-030 R Potential limits to transfers within the SBAA are observed if the response factor (PTDF or OTDF) is 3% or greater and a viable operating procedure is not available. Potential limits to transfer with response factors below 3% may also be observed if the constraint has historically limited or is anticipated to limit transfers in real-time operations. Potential limits to transfer on any other adjacent system in the transmission model that are not on the study path are observed if the response factor is 5% or greater and a viable operating procedure is not available. Reservations and Schedules: Starting with the SERC OASIS power flow cases, SCS incorporates confirmed reservations for the SBAA and any additional transactions provided by the entities in Attachment C, filtered to reduce or eliminate duplicate impacts from transactions using Transmission Service from multiple Transmission Service Providers. When developing the SBAA monthly power flow cases, partial path confirmed reservations which are considered unlikely to flow in certain months based upon historical operating practice or engineering judgment may not be included in those months. To the extent schedules are known, they are included in the power flow cases. Points of Power Injection and Extractions (Sources and Sinks): For transfers originating in the SBAA, SCS models the source as a part of the combined system resources dispatched within the SBAA. For transfers originating outside of the SBAA, SCS reflects the transfer in the interchange with the neighboring area identified on the Point of Receipt (POR), or the aggregate balancing area encompassing the source or Point of Receipt (POR). For transfers sinking in the SBAA, SCS models the sink specified on the transmission service request as part of the load forecast for the SBAA. For transfers sinking outside of the SBAA, SCS reflects the transfer in the interchange with the neighboring area identified on the Point of Delivery (POD), or the aggregate balancing area encompassing the sink or Point of Delivery (POD). Source/sink information POD and POR mapping can be found in the POR-POD_mapping.doc document available on OASIS (link: SOCO POR-POD Mapping). For the PORs of neighboring areas, SCS uses the generation dispatch that is provided by the entities in Attachment C. TRM and CBM: TRM and CBM are not presently modeled in the power flow cases, nor are any facilities de-rated. TRM and CBM are accounted for in the calculation of Firm ATC, as discussed in the ATC section. Effective: December 17, 2013 Page 12 of 24

13 When appropriate to reflect system conditions, SCS may model transfers to represent CBM and/or TRM in the power flow cases. Generation Dispatch: For the areas external to the SBAA, the generation dispatches provided by external entities listed in Attachment C are incorporated into the power flow cases. Internal to the SBAA, SCS utilizes an expected dispatch of the network resources provided by the Load Serving Entities (LSEs) located within the SBAA taking into account any resources that are planned to be unavailable due to generator maintenance outages. For power flow cases used to determine monthly import transfer capability into SBAA for the summer months (June through September), the generation dispatch typically includes the assumption of one critical unit as offline and unavailable. To model transfers to evaluate transfer capability, SCS utilizes a Load to Load Shift, Generation to Generation Shift or a combination of Generation/Load to Generation/Load Shift. To model transfers specific to a particular transmission service request, SCS will model the source/sink as discussed in Points of Power Injection and Extractions (Sources and Sinks) above. Generation and Transmission Outages: Planned generation and transmission outages for both internal and external facilities are incorporated into power flow cases. Outages of external facilities are included to the extent such are provided by the entities in Attachment C. Because outages vary over the course of a month, the outages included in the monthly power flow cases are those scheduled to occur concurrently that are anticipated to materially impact TTC values during the month. Outages from other Transmission Service Providers that cannot be mapped to the Transmission model are not included in the model. SCS evaluates its planned generation and transmission outages to determine a time frame that would result in the greatest overall impact to transfer capabilities for the month being studied. After a time frame is selected, all expected outages in this timeframe are modeled in the power flow case. Customer Demands, Including Interruptible Demands: The customer demand is reflected in the power flow cases which are developed as described under monthly Modeling and Transmission System Topology. For monthly power flow cases, the SBAA load levels are scaled to the higher of each month s average weekday peak from the past two years. Total Transfer Capability (TTC) Values: TTC is the combination of: Effective: December 17, 2013 Page 13 of 24

14 1) Existing commitments for transmission service reflected as base transfers, as indicated in the associated interchange spread sheet, in the power flow model and 2) First Contingency Incremental Transfer Capability (FCITC) which is the amount of transfer capability identified in a transfer analysis, as prescribed in R6 of the current version of MOD-028, in addition to that utilized to serve the base transfers modeled in the power flow base case. FCITC is determined for the paths indicated in Appendix A by increasing generation and/or decreasing load within the source Balancing Authority area and decreasing generation and/or increasing load within the sink Balancing Authority area until an applicable SOL is determined, using the source and sink generation and/or load participation factors defined in the applicable subsystem files. The FCITC value is rounded down to the nearest 10 MW. Stated simply, TTC is determined by adding the applicable base transfers to the FCITC. TTC = FCITC + Base Transfers* *While generally true for imports in import analysis and exports in export analysis, treatment of transfers which may create opposing flows may require additional considerations. See discussion under Reservation Netting Practices. In an effort to provide reliable service by addressing the simultaneous interaction among multiple ATC Paths, SCS performs a simultaneous transfer analysis, in addition to the analysis prescribed in R6 of the current version of MOD-028, on a subset of the ATC Paths listed in Attachment A: SOCO- MISO, SOCO-TVA, SOCO-DUK, SOCO-SCEG, SOCO-SC, MISO-SOCO, TVA-SOCO, DUK-SOCO, SCEG-SOCO and SC-SOCO. This analysis reports the results on an Area Interchange basis as described in the NERC TTC reference document. TTC values are reviewed at least once per month with models and analysis updated as needed to reflect significant changes in system conditions. If more limiting system conditions are identified using the simultaneous transfer analysis on a particular interface, SCS will utilize the simultaneous TTC results as appropriate for system conditions. SCS determines simultaneous TTC values for the northern interfaces which includes MISO, TVA, DUK, SCEG, and SC. SCS simultaneous TTC values determined by SCS are the combination of committed transfer capability, allocated to specific interfaces in accordance with the transmission service commitments, and remaining (incremental) capability, allocated among the northern interfaces. Potential limits to transfer are observed if the response factor (PTDF or OTDF) is 3% or greater and a viable operating procedure is not Effective: December 17, 2013 Page 14 of 24

15 available (see Contingencies and Monitoring ). The limit to transfer is observed for each interface which has a non-simultaneous response factor of 3% or greater. Reservation Netting Practices for TTC/ATC Calculations: As discussed above, TTC is determined from the following general equation: TTC = FCITC + base transfers It is important to understand the relationship of the TTC equation to netting. To simplify discussion, we will refer to an export transfer being included in an import study, though the reverse is possible as well (consideration of an import transfer being included in an export study). The export transfer may create an opposing flow to imports which relieves loading on the limiting element. If so, this loading relief will result in a higher FCITC value. However, the higher FCITC value is possible only if the opposing flow actually occurs in real-time. To be conservative, the TTC equation treats export transfers as negative values causing them to be subtracted from the FCITC and effectively lowering TTC values. This is the default approach used by SCS in determining TTC values. SCS may also assess the following: 1. Do the base exports provide opposing flows that relieve the limiting elements? Base exports which do not provide opposing flows which relieve the identified limiting elements may be excluded from import TTC calculations, allowing higher TTC values to be used. If the base export is expected to result in some partial opposing flow (less than 100%) relief to the limiting element, then it could be appropriate to exclude the corresponding remaining percentage of the base export from the import TTC calculation (i.e., the percentage of the base export that is not expected to provide relief to the limiting element). 2. If the base export provides relief to the limiting element, will the exports (or a portion thereof) actually flow in real-time? Base exports with a high expectation to flow in real-time may be considered for netting purposes. Netting is the practice of not subtracting transfers deemed highly likely to flow in real-time from FCITC. This practice allows for higher TTC values by assuming that helpful opposing flows will be present in realtime. As a result of this assessment, the default approach used by SCS in determining TTC values may be modified to include a portion or all of certain base exports in import TTC calculations and a portion or all of certain base imports in export TTC calculations. Effective: December 17, 2013 Page 15 of 24

16 Daily, Hourly, and Weekly TTC assessments Monthly TTC values are used to initially populate Weekly, Daily and Hourly TTC values. Daily and Hourly TTC values are updated 2-Days Out and more frequently if system conditions warrant. Transfer analysis is performed consistent with the parameters described for Monthly TTC assessments with the following exceptions. 2-Day Out and Day-Ahead o In addition to the models described in the Monthly TTC assessments, state estimation models of real-time snapshots from the Energy Management System (EMS) may be used to develop Daily Models. o A load forecast is determined using a neural network application which considers the weather forecast and historical load values for similar time and weather conditions. Recent historical values are weighted more heavily in the algorithm. o Ambient adjusted ratings may be used. o In the daily transfer analysis, SCS tests all SBAA contingencies of transmission elements 100 kv and above having a PTDF of 1% or greater to the study transfer. SCS also tests all additional facilities that are provided by adjacent entities listed in Attachment C which passed the tests prescribed in MOD-030 R2.1.4., provided that such facilities have a PTDF of 1% or greater to the study transfer and are explicitly represented in the power flow model. Generation and Transmission Outages: Planned generation and transmission outages for both internal and external facilities are incorporated into power flow cases. Outages of external facilities are included to the extent such are provided by the entities in Attachment C. The outages included in the daily power flow cases are those scheduled to occur concurrently that are anticipated to materially impact TTC values during the day. Outages from other Transmission Service Providers that cannot be mapped to the Transmission model are not included in the model. SCS evaluates its planned generation and transmission outages to determine a representative hour that would result in the greatest overall impact to transfer capabilities for the day being studied (often the peak load hour). After an hour is selected, all expected outages in this hour are modeled in the power flow case, provided that they are explicitly represented. Reservations and Schedules: When developing the Daily models, SCS adds all confirmed firm transmission service commitments that are expected to be scheduled for the study timeframe. Confirmed firm transmission service commitments, expected to be scheduled, that are provided by the entities in Effective: December 17, 2013 Page 16 of 24

17 Attachment C are also included. These commitments are filtered to reduce or eliminate duplicate impacts from transactions using Transmission service from multiple Transmission Service Providers. Recalculation Frequency of TTC To provide for reliable service and to meet NERC reliability requirements, SCS routinely updates the transfer capability evaluations as updated information becomes available. Transfer capabilities that are used in the monthly ATC calculations are updated at least once per calendar month. SCS updates transfer capabilities used in daily and hourly ATC calculations at least once within the seven calendar days prior to the specified period. In the event of an unexpected outage of an SBAA 500 kv or higher transmission Facility or an SBAA transformer with a low-side voltage of 200 kv or higher, SCS recalculates all affected transfer capabilities, within 24 hours, provided such outage is expected to last 24 hours or longer. Additional Coordination TTC assessments for PowerSouth: In addition to the requirements contained in the current versions of MOD-001 and MOD-028, TTC values for the AEC- SOCO and SOCO-AEC paths are further coordinated between SCS and PowerSouth. The values resulting from the monthly and daily TTC assessments represent the most limiting SOL between the SBAA and PowerSouth. TTC assessments for peninsular Florida: In addition to the requirements contained in the current versions of MOD-001 and MOD-028, Southern Company Services participates in the Florida-Southern Coordinating Group to develop coordinated transfer capability values between the SBAA and the Florida Reliability Coordinating Council (FRCC). The values resulting from the coordinated monthly and daily TTC assessments represent the most limiting SOL among all participating parties involved Existing Transmission Commitments (ETC): SCS defines ETC as commitments for transmission service which exist at the time a transfer analysis is performed. Transmission service for network and native loads is represented in power flow analyses by modeling forecasted loads and serving them with the expected dispatch of the associated network resources. Firm PTP Transmission Service is represented in the power flow models as previously discussed in Points of Power Injection and Extractions (Sources and Sinks). The modeling treatment is consistent whether the existing transmission service commitment is OATT service or non-oatt (native load or grandfathered) service. Rollover rights are evaluated as a continuation of service in the zero to thirteen months postings unless the renewal deadline has expired. For each particular interface, service type, and time period, ATC is determined by subtracting the Effective: December 17, 2013 Page 17 of 24

18 commitments on that interface from the respective TTC value in accordance with the formulas shown above. Firm ATC calculations consider only firm commitments. Non-firm ATC considers both firm and non-firm commitments Postbacks: Postbacks are positive adjustments to ATC as defined in Attachment C of Southern Companies OATT. SCS s Business Practices may include capacity that is posted back on OASIS as additional ATC as a result of: (i) customers not scheduling service; or (ii) customers redirects of service to other paths Unscheduled Service: Transmission service commitments that are not scheduled (wholly or partially) result in the unscheduled portions being posted back to OASIS in the form of non-firm ATC. For example, if the holder of 100 MW of Daily Firm service on a path schedules only 80 MW during an upcoming hour, the remaining 20 MW will be posted back as non-firm ATC on that path for that hour Short-term Redirect: Firm PTP transmission customers may redirect their transmission service on a firm or non-firm basis, to any path where ATC is available If the redirect is to a path where firm service is available, the firm ATC will be decremented on the new path and firm ATC will be released on the original path If the redirect is to a path where only non-firm service is available, the non-firm ATC will be decremented on the new path; however, the customer will reserve the right to return to the original path and firm ATC will not be released on the original path. Non-firm ATC will be released on the original path Counterflows: Counterflows are the amount of scheduled megawatts ( MW ) associated with the SCS s customers transactions that will flow in the opposite direction on a path (resulting in a reliable reduction of flow on constrained facilities), that SCS determines can effectively be used to increase ATC. It should be noted that counterflows associated with certain types of constraints (e.g., simultaneous transfer capability limits, voltage limits and stability limits) may not provide relief to constrained facilities required to enable a reliable increase in ATC values. The SCS only considers counterflows in the calculation of hourly (non-firm) ATC Transmission Reliability Margin (TRM): TRM is defined in SCS s TRMID. The TRMID also contains SCS s TRM methodology. TRM values are maintained on Southern Companies OASIS Databases used in TRM assessments: The following databases are utilized in the TRM assessment Southern Company Services - Transmission Dynamics Database for Transmission Planning Models SERC Dynamics Study Group Dynamics Database NERC MMWG Dynamics Model Conditions under which SCS uses TRM: SCS reserves TRM only to calculate firm ATC for imports and such capacity is made available to the market on a non-firm basis. Effective: December 17, 2013 Page 18 of 24

19 2.6. Capacity Benefit Margin (CBM): CBM is defined in SCS s CBMID. The CBMID also contains SCS s CBM methodology. CBM values are maintained on SCS s OASIS. Effective: December 17, 2013 Page 19 of 24

20 Attachment C: Transmission Operators and Transmission Service Providers from which SCS Receives Data for Use in Calculating TTC 1. City of Tallahassee 2. Duke Energy Carolinas 3. Entergy 4. Midcontinent Independent System Operator, Inc. 5. Florida Power & Light Co. 6. Florida Reliability Coordinating Council, Inc. 7. Georgia Transmission Corporation 8. JEA 9. Municipal Electric Authority of Georgia 10. PowerSouth Energy Cooperative 11. Duke Energy Florida 12. South Carolina Electric & Gas Company 13. South Carolina Public Service Authority 14. South Mississippi Electric Power Association 15. Southern Company Services, Inc.-Trans 16. Tennessee Valley Authority Effective: December 17, 2013 Page 20 of 24

21 Attachment D: Transmission Operators and Transmission Service Providers from which SCS Receives Data for Use in Calculating ATC 1. Southern Company Services, Inc -Trans (facilitated on Southern Companies OASIS) Effective: December 17, 2013 Page 21 of 24

22 Attachment E: Transmission Operators and Transmission Service Providers to which SCS Provides Data for Use in Calculating Transfer Capability 1. City of Tallahassee 2. Duke Energy Carolinas 3. Midcontinent Independent System Operator, Inc. 4. Florida Power & Light Co. 5. Georgia Transmission Corporation 6. JEA 7. Municipal Electric Authority of Georgia 8. PowerSouth Energy Cooperative 9. Duke Energy Florida 10. South Carolina Electric & Gas Company 11. South Carolina Public Service Authority 12. Tennessee Valley Authority Effective: December 17, 2013 Page 22 of 24

23 Attachment F: Description of the Allocation Processes SCS Uses to Allocate Transfer Capability among Multiple Owners or Users of an ATC Path 1. Allocation Process: The allocation process SCS uses to allocate Transfer Capability (where allocation is done) is governed by the Integrated Transmission System Agreements (ITSAs). The ITSAs are three bi-lateral contracts between Georgia Power Company (a subsidiary of Southern Company) and Dalton Utilities, Georgia Transmission Corporation and Municipal Electric Authority of Georgia. Dalton Utilities, Georgia Power Company, Georgia Transmission Corporation, and the Municipal Electric Authority of Georgia are collectively referred to as the ITS participants. The ITS participants periodically review the Transfer Capability of each Integrated Transmission System (ITS) interface (the ITSAs use the term Interconnection to refer to an interface) with non-sbaas. Each ITS participant and their respective TOP (or TSP) receives an allocation for all ATC Paths in an ITS interface. The ATC Paths in ITS interfaces are listed in the table below. Allocations are applied to the ATC Path s calculated TTC to determine the appropriate TTC for each ITS participant. 2. Allocation Factors: The allocation factors determined by the ITS participants are used to allocate Transfer Capability among ITS participants and other Transmission Owners for an interface with non-sbaas. First, the TTC values for the applicable ATC Paths listed in the table below are multiplied by a set of allocation factors to calculate the TTC MW that are allocated to ITS participants versus the TTC MW that are not allocated to ITS participants. After the total allocation of TTC for all ITS participants has been determined, that value is multiplied by a second set of allocation factors to calculate the TTC MW that are allocated to each ITS participant. 3. ATC Paths with Allocation Factors: The allocation factors are applied to the following ATC Paths in ITS interfaces. 1. AEC-SOCO 2. DUK-SOCO 3. FL-SOCO 4. SC-SOCO 5. SCEG-SOCO 6. TVA-SOCO 7. SOCO-AEC 8. SOCO-DUK 9. SOCO-FL 10. SOCO-SC 11. SOCO-SCEG 12. SOCO-TVA Effective: December 17, 2013 Page 23 of 24

24 Attachment G: SCS s List of Entities (1) to be Notified before Implementing a New or Revised ATCID and (2) to Have Access to the Current ATCID 1. City of Tallahassee 2. Duke Energy Carolinas 3. Entergy 4. Midcontinent Independent System Operator, Inc. 5. Florida Power & Light Co. 6. Florida Reliability Coordination Council 7. Georgia Transmission Corporation 8. JEA 9. Municipal Electric Authority of Georgia 10. PowerSouth Energy Cooperative 11. Duke Energy Florida 12. South Carolina Electric & Gas Company 13. South Carolina Public Service Authority 14. South Mississippi Electric Power Association 15. Tennessee Valley Authority 16. VACAR South Effective: December 17, 2013 Page 24 of 24